Method and device for measuring the phase shift between a periodic signal and an output signal at an output of an electronic component

ABSTRACT

A method and a device for measuring a phase shift between a periodic signal and an output signal at an output of an electronic component. A supply voltage potential is applied to a electronic component, whereby the periodic signal is applied to the output of the electronic component. The current through the supply voltage input is measured, whereby a magnitude of the current corresponds to a phase shift between the periodic signal and the output signal.

BACKGROUND OF THE INVENTION

[0001] Field of the Invention

[0002] The invention relates to the measuring of a phase shift betweenan external periodic signal that is applied to an electronic component,and an internal signal with which data are to be outputted at one ormore outputs of an electronic component.

[0003] Electronic components are often synchronously driven; i.e., dataare routed from one component to the next according to a clock signal.However, the importance of signal transit times and transit times ofclock signals must not be overlooked, particularly for electroniccomponents that are driven with high frequencies. In order to adapt theprocessing of data to the signal delays conditioned by the transittimes, internal reference clock signals exhibiting a phase shiftrelative to the external clock signals are generated in the electroniccomponents. The phase shift can derive from internal signal transittimes in the electronic component and is strongly dependent ontechnology-related fluctuations.

[0004] In order to be able to correctly evaluate the output data in thetesting of the electronic component, it is necessary to determine thephase shift between the external clock signal and the internal clocksignal according to which the data are synchronously outputted by theelectronic component.

[0005] In known testing systems, a time Δt₀ is customarily determined inorder to measure the phase. Δt₀ is a time difference by which anevaluation signal of the testing device must be shifted relative to theclock signal of the testing device in order to correctly logicallyevaluate a data signal or an internal clock signal. The transition ofthe signal from “0” to “1” or vice versa is needed for this. In order tomeasure Δt₀, the evaluating signal of the testing device is varied untilthe transition between the two voltage levels of the signal has beenfound. The search process is time-intensive and must be performed foreach data signal and the internal clock signal.

SUMMARY OF THE INVENTION

[0006] It is accordingly an object of the invention to provide a methodand a device for measuring the phase shift between a periodic signal andan output signal at an output of an electronic component which overcomethe above-mentioned disadvantages of the prior art methods and devicesof this general type, in which the device provides an improved methodwith which the phase shift between the external clock signal and theinternal clock signal (that is to say, the output data signal) inelectronic components, particularly in the testing of the electroniccomponent, can be determined.

[0007] With the foregoing and other objects in view there is provided,in accordance with the invention, a method for measuring phase shifts.The method includes providing an output driver having an output and aswitching device connected to a supply voltage and to the output. Anoutput signal is applied to the output driver. The supply voltage isswitched through to the output in dependence upon the output signal. Aperiodic signal is applied to the output of the output driver. A currentthrough the switching device is measured and a phase shift between theperiodic signal and the output signal is determined in dependence on thecurrent measured.

[0008] According to a first aspect of the invention, a phase-sensitivemeasuring element is utilized for measuring the phase shift between theperiodic signal and the output signal. The phase-sensitive measuringelement is configured to measure an electrical quantity representing anaverage value of the phase shift.

[0009] The advantage of utilizing a phase-sensitive measuring element isthat the phase shift between the periodic signal and the output signalcan be determined more exactly. In the prior methods, the phase shift isdetermined by timing, with the measured time being considered inrelation to the period duration of the clock signal.

[0010] At very high clock signal frequencies, the timing is generallyimprecise, because it is carried out by single measurements in discretesteps. The imprecision is determined mainly by the imprecision of theindividual measurement steps and the size of the discrete steps. Anotheradvantage is that the phase shift is automatically detected, and thevalue of the phase shift can be evaluated as an electrical quantity, forinstance in the testing device, without unnecessarily prolonging thetesting sequence by an expensive measuring sequence.

[0011] According to another aspect of the invention, a method isprovided for measuring the phase shift between the periodic signal andthe output signal at an output of an electronic component. The outputsignal is applied to an output driver. The output driver contains aswitching device, which is connected to a supply voltage and the output,it being possible to switch the supply voltage through to the output independence upon the output signal. The periodic signal is applied to theoutput. The current through the switching device is measured, and thephase shift between the periodic signal and the output signal iscalculated as a function of the measured current.

[0012] In accordance with an added mode of the invention, the currentmeasured is averaged which gives a more reliable result.

[0013] In accordance with an addition mode of the invention, there arethe steps of using an external clock signal as the periodic signal andusing an internal clock signal for the output signal.

[0014] In another aspect of the invention, a device is provided formeasuring the phase shift between the periodic signal and the outputsignal that can be applied at an output of an electronic component by anoutput driver. The output driver contains a switching device that isconnected to a supply voltage terminal and to the output in order toswitch the supply voltage terminal through to the output in dependenceupon the output signal. The device contains a drive circuit for applyingthe periodic signal to the output of the electronic component. Thedevice further contains a supply voltage source, which can be connectedto the supply voltage terminal of the electronic component by way of acurrent measuring device. In this manner, the phase shift between theperiodic signal and the output signal can be measured as in dependenceon a current that is measured with the aid of the current measuringdevice.

[0015] The advantage of the invention is the possibility, inconventional testing devices, to measure the current flow into and outof the supply voltage inputs, on one hand, and to connect the terminalsof the testing device to the electronic component in such a way that asignal can be driven to an output of the electronic component, on theother hand. This is possible because each connection to the testingdevice can be driven as an input and as an output under the control ofthe respective test program. In this manner, it is possible to determinethe phase shift from the quantity of the current flowing into the supplyvoltage input.

[0016] In prior methods, the phase shift is performed by a timingoperation, whereby the measured time is considered in relation to theperiod duration of the clock signal, and the phase shift is determinedtherefrom. In contrast, the present method has the advantage that it canbe applied even given very high clock signal frequencies, i.e. givenvery small period durations. The timing operations become imprecise asthe time differences to be measured become smaller, and therefore thephase shift can no longer be precisely measured. In contrast, theinventive method and device have the advantage that, the phase shiftover several periods is automatically averaged, and the method isprecise even given high frequencies and small phase shifts.

[0017] In a preferred embodiment, it is provided that a supply voltageinput of the switching device is connected to a capacitance component,whereby an additional output of the capacitance component is connectedto a fixed voltage potential. The capacitance component smoothes thecurrent shape, thereby making it possible better to determine theaverage value of the phase shift.

[0018] In accordance with an added feature of the invention, a terminalfor carrying a constant d.c. voltage potential is provided. Acapacitance component having a first terminal is coupled to the supplyvoltage terminal and a second terminal is connected to the terminalcarrying the constant d.c. voltage potential.

[0019] In accordance with another feature of the invention, a testingdevice is provided which contains the drive circuit.

[0020] In accordance with an additional feature of the invention, thesupply voltage terminal is one of two supply voltage terminals eachsupplying a supply voltage, and the switching device is connectedbetween the two supply voltage terminals.

[0021] In accordance with a further feature of the invention, theswitching device has a transistor.

[0022] With the foregoing and other objects in view there is provided,in accordance with the invention, a method of measuring a phase shift.The method includes providing a phase-sensitive measuring element, andsupplying the phase-sensitive measuring element with a periodic signaland an output signal. The output signal is provided at an output of anelectronic component connected to the phase-sensitive measuring element.The phase-sensitive measuring element is used to measure an electricalquantity representing an average value of the phase shift between theperiodic signal and the output signal.

[0023] In accordance with an added mode of the invention, there are thesteps of measuring a voltage as the electrical quantity, and providingthe phase-sensitive measuring element with a voltage measuring devicefor measuring the voltage.

[0024] In accordance with another mode of the invention, there is thestep of providing the phase-sensitive measuring element with anexclusive-or gate with two inputs, the two inputs receiving the periodicsignal and the output signal.

[0025] In accordance with a concomitant mode of the invention, there isthe step of providing the phase-sensitive element with an analog phasedetector containing a step recovery diode.

[0026] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0027] Although the invention is illustrated and described herein asembodied in a method and a device for measuring the phase shift betweena periodic signal and an output signal at an output of an electroniccomponent, it is nevertheless not intended to be limited to the detailsshown, since various modifications and structural changes may be madetherein without departing from the spirit of the invention and withinthe scope and range of equivalents of the claims.

[0028] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a graph showing a method for determining a phase shiftaccording to the prior art.

[0030]FIG. 2A is a block diagram of a first preferred embodiment formeasuring the phase shift with an aid of a phase-sensitive elementaccording to the invention;

[0031]FIG. 2B is a graph of a signal curve for input and output signalsof the phase-sensitive element according to FIG. 2A; and

[0032]FIG. 3 is a circuit diagram of a second preferred embodiment formeasuring the phase shift with the aid of a testing device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown how a phase shiftbetween an external clock signal and an internally generated clocksignal (i.e. an internally generated item of data) is measured accordingto the prior art. In conventional testing methods, a testing devicedetermines a time between a leading edge of the external clock signaland a subsequent leading edge of the internal clock signal or datasignal.

[0034] The time is determined in that a sampling signal, with which theinternal clock signal (data signal) is sampled, is generated with avariable time delay relative to the leading edge of the external clocksignal. By varying the time delay Δt of the sampling signal, it ispossible to ascertain the delay with which the leading edge of theinternal clock signal (data signal) follows the leading edge of theexternal clock signal. A phase shift φ is determined by considering themeasured time difference Δt₀ in relation to the overall cycle length ΔT₀of the external clock signal. The phase shift φ is determined accordingto the following formula:${\varphi ({rad})} = \frac{{2 \cdot \pi \cdot \Delta}\quad t_{0}}{\Delta \quad T_{0}}$

[0035] In order to detect the corresponding edge of the internal clocksignal (data signal), the signal is sampled multiple times in order toprecisely determine the transition (i.e. the time difference Δt₀) of thesignal from “0” to “1” or vice versa. The search process must beperformed for each internal clock signal (data signal) and is thereforetime-intensive.

[0036]FIG. 2A represents a block circuit diagram of a preferredembodiment of the invention. In a phase-sensitive element 1 an externalclock signal CLK and an internal clock signal DQS (i.e. data signal DQ),which is outputted at an output of an electronic component 4, areassociated with one another. The external clock signal CLK can besupplied by a testing device 3 and is fed to the component 4. At anoutput of the phase-sensitive element 1 is an output signal XOR, atwhich the phase shift between the external clock signal CLK and theinternal clock signal DQS (data signal DQ) can be read.

[0037] In a possible embodiment, the phase-sensitive element 1 includesan exclusive-or gate at whose output impulses are outputted with thefrequency of the clock signals (as represented in FIG. 2B), whereby alength of the impulses is determined by the phase shift of the signalsto one another.

[0038] The output signal XOR of the phase-sensitive element 1 isfiltered by a low-pass filter 2, so that a substantially constant analogoutput signal A is formed, which corresponds to a voltage level. Thevoltage level can then be measured in the testing device 3 and thenrepresents a measure of the phase shift of the external clock signalsCLK and the internal clock signals DQS (data signals DQ). In thismanner, the average phase shift φ between the signals can be determined,with fluctuations between the phase shifts (jitter) being averaged outby the low-pass filter.

[0039] The voltage level can be measured by a voltage measuring device3′, which can be located in the testing device 3, for example. Thephase-sensitive element 1 can be connected to the electronic component4, though it can also be integrated into the electronic component 4. Asphase-sensitive elements, it is also possible to utilize log-inamplifiers (available from Stanford Research Systems), an analog phasedetector employing a step recovery diode, a digital phase detector, andso on.

[0040]FIG. 3 represents another preferred embodiment for measuring thephase shift φ between the external clock signal and the internal clocksignal DQS (data signal DQ) of an integrated circuit. The integratedcircuit can be constructed in the form of an SGRAM or DDR-SDRAM. Thephase shift is performed with the testing device 3 (automated testequipment ATE). The testing device 3 is capable of supplying theintegrated circuit 4 with voltage supplies V_(s), whereby the currentflowing through the voltage supplies V_(s) can be measured with the aidof current measuring devices 11, 12 located in or downstream from thetesting device 3.

[0041] The integrated circuit 4 contains an output drive circuit 5,which includes a first transistor T1 and a second transistor T2. A firstterminal of the first transistor T1 is connected to a first supplyvoltage level V_(DD) via the voltage supply V_(S) of the testing device3, and a second terminal of the first transistor T1 is connected to thesignal output A. A first terminal of the second transistor T2 isconnected to a second supply voltage level V_(ss), and a second terminalof the second transistor T2 is connected to the signal output A. Thefirst and second transistors T1 and T2, respectively, are of differentconductivity types. The digital internal clock signal DQS (i.e. datasignal DQ) is supplied to control inputs of the first and secondtransistors T1 and T2 has the effect that either the first transistor T1or the second transistor T2 becomes conductive, as a result of whicheither the first supply voltage level V_(DD) or the second supplyvoltage level V_(SS) is applied to the signal output A.

[0042] The testing device 3 is so connected to the integrated circuit 4by way of a drive circuit 7, that the external clock signal CLK isdriven to the signal output A of the integrated circuit 4. In thismanner, the external clock signal CLK and the internal clock signal DQS(data signal DQ) at the control inputs of the first and secondtransistors T1 and T2 are driven against one another.

[0043] When the external clock signal CLK and the internal clock signalDQS (data signal DQ) at the control inputs of the first and secondtransistors T1 and T2 are in phase, the transistors T1, T2simultaneously switch at that instant when the signal driven onto thesignal output A by the testing device 3 changes from high to low levelor vice versa. As a result, an identical voltage potential is present atthe two terminals of the respective first or second transistor T1 and T2when the transistor is conductive. A current measuring operation at therespective supply voltage input then shows no substantial current flowthrough the transistor T1 or the transistor T2.

[0044] If the external clock signal CLK and the internal clock signalDQS or data signal DQ are phase-shifted relative to one another, thefull voltage swing is present across the respective transistor for theperiod between the corresponding clock edges, and the transistor is thenswitched to conduct. In this way, a current flows across the respectivetransistor T1, T2 for a period corresponding to the time quantity of thephase shift φ. Thus calculated, the phase shift φ can be utilized in thetesting device 3 to set signal delay elements so that a phase shift φbetween signals can be compensated.

[0045] In order to evaluate the periodically pulsed current flow,capacitors 6 are provided at the supply voltage terminals of theintegrated circuit 4, which smooth the voltage shape and thus thecurrent shape. The capacitors 6 are parallel to the supply voltageterminal and a ground potential GND. As a result, a nearly constantcurrent flows, whose magnitude is dependent upon the magnitude of thephase shift. The capacitors 6 for buffering the supply voltages aretypically provided inside the chip in the form of a chip surface regionthat is constructed as a capacitor or even by the capacity of the supplyvoltage lines. The supply voltage potentials V_(DD), V_(SS) that areprovided by the testing device 3 may also be buffered by a capacitance.

[0046] The inventive features disclosed in the foregoing description andin the claims and drawings can, either individually or in anycombination, be essential to the invention in its various embodiments.

I claim:
 1. A method for measuring phase shifts, which comprises the steps of: providing an output driver having an output and a switching device connected to a supply voltage and to the output; applying an output signal to the output driver, the supply voltage being switched through to the output in dependence upon the output signal; applying a periodic signal to the output of the output driver; measuring a current through the switching device; and determining a phase shift between the periodic signal and the output signal in dependence on the current measured.
 2. The method according to claim 1, which comprises averaging the current measured.
 3. The method according to claim 1, which comprises using an external clock signal as the periodic signal.
 4. The method according to claim 1, which comprises using an internal clock signal for the output signal.
 5. A device for measuring phase shifts, the device comprising: a supply voltage terminal for supplying a supply voltage source; a component containing an output driver having a switching device coupled to said supply voltage terminal, said output driver having an output functioning as an output of said component, said output driver switching the supply voltage source through to said output in dependence upon an output signal applied to said output driver; a drive circuit connected to said output and applying a periodic signal to said output; a current measuring device connected between said supply voltage terminal and said switching device for supplying the supply voltage source to said switching device, a phase shift between the periodic signal and the output signal being measurable as a function of a current measured with an aid of said current measuring device.
 6. The device according to claim 5, further comprising: a terminal for carrying a constant d.c. voltage potential; and a capacitance component having a first terminal coupled to said supply voltage terminal and a second terminal connected to said terminal carrying the constant d.c. voltage potential.
 7. The device according to claim 5, further comprising a testing device containing said drive circuit.
 8. The device according to claim 5, wherein said supply voltage terminal is one of two supply voltage terminals each supplying a supply voltage, and said switching device connected between said two supply voltage terminals.
 9. The device according to claim 5, wherein said switching device has a transistor.
 10. A method of measuring a phase shift, which comprises the steps of providing a phase-sensitive measuring element; supplying the phase-sensitive measuring element with a periodic signal and an output signal, the output signal provided at an output of an electronic component connected to the phase-sensitive measuring element; and using the phase-sensitive measuring element to measure an electrical quantity representing an average value of the phase shift between the periodic signal and the output signal.
 11. The method according to claim 10, which comprises: measuring a voltage as the electrical quantity; and providing the phase-sensitive measuring element with a voltage measuring device for measuring the voltage.
 12. The method according to claim 11, which comprises providing the phase-sensitive measuring element with an exclusive-or gate with two inputs, the two inputs receiving the periodic signal and the output signal.
 13. The method according to claim 11, which comprises providing the phase-sensitive measuring element with an analog phase detector containing a step recovery diode. 